Anemia

1. What every clinician should know

Clinical features and incidence

Definition: Hemoglobin (Hgb) concentration lower than 11 g/dL in the first and third trimester, or lower than 10.5 g/dL in the second trimester.

Epidemiology: 23% of pregnant women in industrialized countries and 52% of pregnant women in non-industrialized countries.

The most common cause of maternal anemia is iron deficiency (75% of cases).

As anemic patients are usually asymptomatic, this condition may often be undiagnosed. Therefore, all pregnant women should have an Hgb and mean corpuscolar volume (MCV) evaluated.

The key issue in anemia evaluation is the definition of the underlying mechanism, which leads to different therapies and different clinical implications.

Women with chronic mild anemia may go through pregnancy and labor without symptoms. Symptoms occur when anemia becomes moderate to severe or when it has a rapid onset without the possibility of compensation.

Cardiovascular attempts at compensation: increased cardiac output and heart rate, which cause palpitations and tachycardia; in case of severe anemia these compensatory mechanisms are inadequate to deal with Hgb reduction and can lead to circulatory decompensation, with acidosis, pulmonary edema and death. When Hgb is lower than 5 g/dL, cardiac failure occurs in a third of cases; therefore, signs of decompensation are an indication for urgent treatment.

The underlying cause.

Pathophysiology

The most common cause of maternal anemia is iron deficiency (75% of cases). Some degree of iron deficiency is physiologic during gestation and is related to hemodilution, due to which Hgb concentration reaches the nadir at 24-32 weeks. However, the requirements for absorbed iron increase gradually through gestation, from 0.8 mg/day in the first trimester to 7.5 mg/day in the third trimester. The absorbed iron is used to (a) expand the erythrocyte mass; (b) compensate for iron losses (i.e. blood losses during delivery); and (c) ensure adequate oxygenation and iron intake to the fetus. This request can not be suited only by diet, so a considerable amount of iron is recycled from the body’s iron reserves.

About 42% of fertile women have small iron reserves even before pregnancy; further iron demand causes the depletion of iron storages and consequently anemia.

2. Diagnosis and differential diagnosis

Initial evaluation: complete blood count (CBC) with Hgb and MCV. Anemia is defined as Hgb concentration lower than 11 g/dL in the first and third trimester,or lower than 10.5 g/dL in the second trimester. Severe anemia is defined as Hgb concentration lower than 8.5 g/dL Physiologic changes that occur during gestation should not be confused with anemia: during pregnancy, the increase in plasma volume of about 50% is only partly compensated by an increase in the erythrocite mass of about 25%, resulting in hemodiluition, which leads to an alteration of some blood tests even in non-anemic pregnant women. (Figure 1)

Certain types of congenital anemias are most frequently found in specific ethnic groups; therefore, all individuals of African ancestry should have a hemoglobin electrophoresis.

Microcytic anemia

First, rule out iron deficiency obtaining serum ferritin. If the serum ferritin is less than 12 ng/mL, there is an iron deficiency. If it is greater than 20 ng/mL, obtain Hgb electrophoresis. A pathological electrophoresis: hemoglobinopathies. If the electrophoresis is normal, suspect α-thalassemia trait, anemia of chronic disease (elevated PRC protein and free erythrocyte protoporphyrine) or aplastic anemia (bone marrow). (Figure 2)

A nutrition consult should be obtained for patients with iron, folate or Vitamin B 12 anemia.

4. Complications

Maternal consequences

Severe anemia is the cause of 40% of maternal deaths in undeveloped countries.

Anemia makes the immune status of pregnant women worse: prevalence of morbidity due to infections is doubled in women with Hgb below 8 g/dL; anemia, even if mild, is associated to asymptomatic bacteriuria, often refractory to treatment.

Fetal consequences

A fall in maternal Hgb below 11 g/dL is associated with a significant rise in perinatal mortality rate (two- to three-fold increase if Hgb is less than 8 g/dL, eight- to 10-fold increase if Hgb is less than 5 g/dL);

Hgb less than 8 g/dL is associated with a significant fall in birthweight due to increase in prematurity rate and intrauterine growth retardation.

Anemia and iron deficiency in the mother are not associated with significant degree of anemia in the baby; however, newborns of anemic women have low iron stores and are fed with low iron content-breast milk; thus a high proportion of these infants become anemic by six months.

Most of the adverse outcomes of anemia can be minimized by keeping Hbg values greater than 8.5 g/dL. Thus, therapy must be started immediately: with oral iron therapy reticulocytosis should be observed after 7-10 days and the Hgb can rise by as much as 1 g/week in severely anemic patients.

5. What is the evidence for specific management and treatment recommendations

"Centers for Disease Control and Prevention. CDC criteria for anemia in children and childbearing-aged women". MMWR.
vol. 38. 1989. pp. 400.

(Brief review of changes in hemoglobin and hematocrit in pregnancy; useful table of normality values throughout pregnancy.)

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